1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for etching a metal film containing aluminum using a hard mask, and a method for forming an interconnection line for a semiconductor device using the same.
2. Description of the Related Art
An interconnection line is a film material corresponding to the topmost film of a semiconductor device and it electrically connects devices after each device is completed. The main purposes of the interconnection line are either for connecting a PMOS or NMOS transistor to a bit line, or for connecting a cell to another cell. To manufacture a high-speed device, it is preferred that a low-resistivity material is used for an interconnection line. Thus, aluminum (Al), having the lowest resistivity among widely known materials, or its alloys (referred to as a "metal containing Al" hereinafter) are mainly used.
Since Al has excellent conductivity but is structurally weak at high temperatures, a protective film must be formed on the interconnection line formed of a metal containing Al, by a low pressure chemical vapor deposition (LP-CVD) method. Also, if the metal film containing Al is etched, the photoresist must be formed thickly, since the etching selectivity to photoresist is poor. Further, to allow high-speed operation of the semiconductor device, the metal film containing Al must be as thick as 5,000.about.8,000.ANG.. Thus, in order to etch the metal line containing Al, a highly corrosive etchant must be used, i.e., one having a high etch rate. However, such an etchant is absorbed into the photoresist, causing corrosion in the metal line after etching.
Also, if the photoresist is formed thickly, the throughput is lowered and it is difficult to control the photoresist. Thus, a poor pattern profile is generated due to phenomena produced after the photolithography process, such as residue, notching or slope, and phenomena produced in the metal line after the etching process, such as thinning, bridging or variation in line widths. Particularly, when the semiconductor is highly integrated, the line width of the interconnection line must be reduced. However, it is impossible to reduce the line width of the metal line efficiently using the thick photoresist as in the conventional art.
In forming an interconnection line formed of a metal containing Al, using a photoresist, to avoid diffused reflection from the Al layer there is a widely known method forming the Al line by forming an anti-reflection film on the metal film containing Al by depositing titanium nitride (TiN) or titanium tungsten (TiW), and then forming a photoresist pattern on the anti-reflection film.
The photoresist used in the above-described process is as thick as 18,000.about.21,000 .ANG.. However, in view of processing characteristics, the etching selectivity of the metal film containing Al to the photoresist does not exceed 3:1. Also, the profile of the photoresist pattern is not vertical, but is inclined to some extent. Further, since the photoresist at the edge of the Al film is much thinner than the other portions, the pattern of the metal film containing Al is thinned, and the margin of the photolithography is reduced.
To solve these problems, there has been proposed a process of injecting a hard material film (oxide group) which can serve as a buffer between the metal film containing Al and the photoresist film. However, this process also needs a photoresist film of 12,000.about.16,000 .ANG.thick. Also, if the thickness of the metal film containing Al is greater than or equal to 6,000 .ANG., the process is not effective. Further, during this process, the metal film containing Al is etched when the photoresist exists. Thus, when etching the metal film containing Al, the photoresist must be removed simultaneously in the same machine, to minimize the corrosion caused by a strongly corrosive etchant. However, to this end, since a separate chamber for removing the photoresist must be installed in a chamber for etching the metal film containing Al, it is quite difficult to maintain and operate the facility.